Time-of-flight (TOF) is a technique used to determine the distance to an object or objects in a three-dimensional scene. Further the technique can be used to construct three-dimensional representations of an object or a three-dimensional scene. TOF-based optoelectronic modules frequently employ a modulated light source, a series of optical elements, and a demodulation pixel or demodulation pixel array. Modulated light projected from a modulated light source onto an object in a scene may be reflected to an imaging assembly and focused onto a demodulation pixel. The demodulation pixel and supporting circuitry, may detect a phase shift in the reflected light, wherein the phase shift may be further correlated to the distance the light traveled; specifically, the detected phase shift is the phase shift in the modulated light that transpires when the modulated light travels from the light source to the object and is reflected back to the TOF module. Accordingly, the phase shift (i.e., phase delay) is proportional to the transit time as expressed below:
      t    tof    =      -                  ϕ        tof                    2        ⁢        π        ⁢                                  ⁢                  f          mod                    where ttof is the time-of-flight, ϕtof is the phase shift of the modulated light signal, and the respective modulation frequency is fmod. The distance to the object (Rtof) can then be calculated according to the following:
      R    tof    =                    t        tof            ·      c        2  where c is the speed of light. Alternatively, the round trip time can be directly measured in order to calculate the distance to the object.
Other techniques may be employed for determining distances to objects in a scene such as triangulation. Triangulation-based optoelectronic modules often use a light source, a series of optical elements, and a pixel array. As above, light projected from the light source and reflected by an object in a scene may be focused onto the pixel array via the optical elements. Distance to the object then is determined via a standard triangulation technique where distance is determined from the focal length (i.e., on-axis focal length) of the series of optical elements, the position of the pixel on which the reflected light is focused (e.g., as a spot), and the baseline distance between the optical axis (co-axial with the on-axis focal length) and the illumination source. A conventional triangulation equation is described below wherein Rtri is the distance information obtained by the triangulation measurement; f is the on-axis focal length; b is baseline; xpix is the location of the pixel on which the reflected light is focused (e.g., a spot of light) from the optical axis (co-axial with the on-axis focal-length); α is the angle between the emitted signal and the measurement axis:
      R    tri    =            f      ·      b                      x        pix            +              f        ⁢                                  ⁢                  tan          ⁡                      (            α            )                              Further, if α=0 the formula simplifies to Rtri=(f×b)/xpix).
The TOF approach can yield superior distance data for some applications while the triangulation approach may be better suited to other applications. For example, applications that require distance measurements of about 1 cm or less can be well-suited to optoelectronic modules that employ the triangulation approach while applications that require distance measurements greater than about 1 cm can be well-suited to optoelectronic modules that employ the TOF approach as described above. The distance resolution of both the TOF and triangulation approached outlined above is limited in part by the pixel array resolution. Further, distance resolution is inaccurate to the extent that the pixel, on which light is focused, is of finite dimensions. Light may be focused on the center or edge of the pixel, for example, but this physical difference in focused-light position is not considered in state-of-the-art TOF or triangulation approaches.
Moreover, the TOF approach can suffer from multi-path measurement inaccuracies. For example, modulated light incident on an object may reflect from multiple surfaces at respective different distances; accordingly, different phase shifts may be recorded for the same object obfuscating its true distance. Accordingly, an approach needs to be implemented in order to mitigate multi-path measurement inaccuracies and to improve distance resolution as outlined above.